The present invention relates to a seal between two components such as a sliding shaft and a surrounding sleeve to separate two chambers, such as annular sleeve chambers, supplied with fluids at different pressures.
It is often necessary to utilize a seal between a sleeve and a shaft which is slidably mounted in the sleeve so as to traverse along its longitudinal axis. The shaft may be actuated by the pressure differential between fluids applied to the ends of the shaft. Present seals suffer from the drawback that the sealing action between the shaft and the sleeve is achieved by radial friction between the sealing member against one or the other of the components. While such radial friction may be acceptable for a shaft rotating within the sleeve, it is not acceptable for a shaft which traverses along its longitudinal axis within the sleeve. In the latter case, it is more desirable to achieve the sealing effect by forcing the seal member against a radial side of a groove in which it is located.
French Pat. No. 1,113,528 discloses an O-ring seal located within a groove formed in the shaft and forced against the surrounding sleeve by a second, clamping O-ring. The two O-rings are separated by a metal grille which permits the fluid to pass into the groove such that the relatively high pressure of the fluid will contribute to the sealing force against the sleeve wall.
This seal has not entirely alleviated the aforementioned problems, since, being toroidal in shape, the seal rolls upon itself during shaft translation and, due to the high pressures in the groove, may degrade faster due to contact between it and the metal grille. Such a drawback may be acceptable when the seal is utilized as a piston packing, as shown in U.S. Pat. No. 1,479,089 to Short, but cannot be acceptable in those instances where the sliding shaft must operate with relatively low control pressures. Furthermore, these prior art seals rub against the cylindrical sleeve in direct proportion to the pressure in the high pressure chamber.
It is difficult, if not impossible, to utilize these devices on small diameter, translating shafts, especially when such shafts are controlled by relatively low control pressures compared to the pressures in the chambers which must be separated by the seal. Such applicability is even less in those cases where the pressure in one of the chambers is significantly higher than that in the other.
French Pat. No. 1,509,034 discloses a seal having sealing members with frusto-conical surfaces which mutually cooperate with each other and with an inner spring that forces the jamming member against the sealing member with a wedge effect. This provides radial compression of the sealing member against the cylinder surrounding the shaft and an axial pressure against a lateral side of the groove.
Although such a device is preferable to the previously described O-ring seal, since it provides an axial component of the friction force, it still requires a third member, in addition to the sealing and jamming members, to assure the compression of the jamming member against the sealing member. The three part sealing device, therefore, presents difficulties when required to seal small diameter shafts.